Fuel cells have been used for years to produce electricity through a spontaneous chemical reaction between a fuel and an oxidant in the presence of a catalyst. Fuel cells generally comprise an electrolyte, either solid or a liquid material, which is in contact with and sandwiched between an anode and a cathode electrode. During operation a fuel, generally in a gaseous state, is introduced into the interface between the anode and the electrolyte and an oxidant, also generally a gas, is introduced simultaneously into the interface of the cathode and the electrolyte, where the spontaneous reaction takes place to produce electricity.
To produce large amounts of electricity it is common practice to stack a number of these cells together. In forming a stack of cells it is important that the stack be stable and sealed so that as it is operating or being transported none of the gases or electrolyte (if liquid) is allowed to either escape from the cell stack or cross over from one cell to another. Therefore, the cell stack is typically held under a compressive load to maintain this integrity using tierods incorporated into a cell stack frame. In addition, the fuel cell stack frame is then mounted onto a rigid support frame to give greater support to the fuel cell stack, particularly protection against lateral movement which may occur during transport of the stack or in the event of an earthquake or other similar forces. The rigid support frame is also electrically insulated from the fuel cell stack therefore protecting persons coming near the fuel cell stack from possible contact with the electrically live stack.
A typical fuel cell stack mounting apparatus is shown in FIG. 1 in which a fuel cell stack assembly 4 is positioned within a fuel cell stack holder frame 6 comprising a top end plate 8 and a bottom end plate 10 each positioned at the opposite end of the cell stack assembly 4 and perpendicular to the electrodes 12. The compressive forces are applied through the four tie rods 14 which are positioned one each at the corners 16 of the top end plate 8 and descending substantially perpendicular to the cell electrodes 12 to the mirror image corners 18 of the bottom end plate 10. The tie rods are attached at each of the corners of the top and bottom end plates 16 and 18 by passing a threaded end portion of the tie rod 14 through an opening in the corner and are fixed in place via threaded nuts 20. A dielectric washer 22 is placed between the nut 20 and the bottom end plate surface 24 and a dielectric sleeve 26 surrounds the tie rod portion in contact with the bottom and top end plate 10, 8 as it passes through the hole. The fuel cell stack holder frame 6 is then mounted onto a rigid fuel stack mounting frame 27. The mounting frame 27 comprises a rigid box-like structure having top beams 28 bottom beams 30 and two or more side or corner beams 32, 34. The top end plate 8 of the fuel cell frame 6 is horizontally affixed to the top beam 28 of the fuel cell rigid frame 27 by dielectric mount 36 and the bottom plate 10 of the fuel cell stack frame 6 is affixed to the bottom beam 30 of the rigid frame 27 by four ceramic insulating members 38.
This structure offers support for the fuel cell stack and maintains a safe electrically insulated structure to permit safe transport of the fuel cell stack and to prevent damage to the fuel cell in the event of earthquake or other catastrophe. However, the use of the ceramic insulators to mount the fuel cell stack has certain shortcomings when the fuel cell stack is moved in that the insulators are high in compressive strength, but have a very low flex tolerance so that when the stack is subjected to horizontal pressures or the frame is deflected by external loads the insulators may crack, and therefore need to be replaced. This most often happens during transport of the cell stack to the operation site.
Therefore, what is needed in this art area is an improved insulating and mounting structure between the fuel cell frame and rigid support frame which is cost effective and durable, and preferaby will permit lighter weight rigid frames to be used.